146 Composition of Watei's of Land-Drainage and of Rain. 



attribute to such removal far more force than to the occasional 

 and uncertain influence of rain. 



There is another circumstance that points to the same con- 

 clusion. Every acre of ground which allows water to percolate 

 freely, benefits equally by the nitric acid and ammonia of 

 rain. But whence comes the additional luxuriance which vege- 

 tation puts on when the land is abundantly worked ? whence 

 the Lois Weedon crops ? Obviously Mr. Smith cannot be satis- 

 fied with the ammonia of rain, he must have some from the air 

 also ; and he does get it from the air in far greater quantity than 

 the rain could furnish.* 



If we examine the Table we shall find the facts to bear out 

 this view. There is a general, though not uniform relation 

 between the quantity of ammonia and nitric acid in the month, 

 and the quantity of rain that has fallen in that month. Thus in 

 July we have the largest rain-fall (157,713 gallons), and by far 

 the largest cjuantity of nitrogen (8615 grs.). In October the 

 next largest fall of rain, accompanied with a corresponding 

 (Quantity of nitrogen. In April we have the smallest rain-fall 

 and the smallest quantity of nitrogen ; and January follows it 

 exactly in the same relation. 



That the rain-fall and nitrogen are not more closely related in 

 quantity is probably due to a modification, which the com- 

 parative number of times at which the rain falls would intro- 

 duce."!" The bearing which the figures in the foregoing Table 

 have upon the drainage question may be stated in two words. 

 In the first place, by comparing them Avith those given in the 

 Table of drainage-water, we find that, as far as ammonia is con- 

 cerned, the quantity falling in rain greatly exceeds that which 

 passes off by the drains ; thus, although in no case do we find 

 ammonia in drainage-water to a greater extent than 0"019 per 

 gallon, in rain-water we have no instance where it is less than 

 0*05 ; whilst the mean is 0'086, or four times as much as the 

 largest amount in drainage-water. It is obvious, therefore, that 

 instead of being an agent for the abstraction of ammonia from 

 the soil, rain, on the contrary, carries off (by drainage) less than 

 it brings ; a fact again proving the power of the soil in absorption. 

 But with nitric acid it is different. The quantity of this sub- 

 stance present in rain-water is not enough to account for that 

 found in any one of the drain- waters examined ; and if we take 



* Mr. Smith habitually expresses his obligations to the dew, as a more steady 

 benefactor than the rain, in much the same terms as might express the relation of 

 " daily bread " to an occasional feast. — C. W. H. 



t It has been usual to suppose that the nitric acid of the air is due to electrical 

 action. If so, it is obvious that this force is in continual exercise, since -we find 

 nitric acid present in the rain of every month of the year. 



